1. The Field of the Invention
The present invention relates to an apparatus and a method for controlling a glow plug, and more particularly to an apparatus and a method for controlling electronic power supplied to the glow plug so as to assure activation and running in a steady state of a diesel engine of an automotive vehicle whenever an operator of the automotive vehicle turns key switch on.
2. Description of the Prior Art
A Diesel engine is substantially different from a sparked ignition internal combustion engine in that the diesel engine does not have a sparking device such as a spark plug which is provided in the sparked ignition internal combustion engine. In the diesel engine, fuel is ignited and a piston of the engine cylinder is driven when fuel and hot compressed air are mixed in the engine cylinder. For this ignition to occur effectively, the engine must be brought to a temperature at or above a minimum ignition temperature for a mixture of fuel and hot compressed air. One method to enhance reliability of starting the diesel engine especially in a cold season is to install a glow plug in each cylinder and to operate the glow plug to heat the mixture of fuel and hot compressed air in the cylinder head, thereby assuring starting of the diesel engine.
A glow plug generally uses a resistance heater. This glow plug is attached to an engine block of the diesel engine such that a tip of the resistance heater is positioned in the combustion chamber or cylinder. The mixture of fuel and hot compressed air (which may be abbreviated as the “fuel-air mixture” in the following) has an operating temperature at or above which the diesel engine can achieve ignition and run efficiently. When the fuel-air mixture is injected to the combustion chamber after the temperature of the resistance heater of the glow plug is raised up to an operating temperature, the temperature of the fuel-air mixture can reach the operating temperature thereof. In this situation where the temperature of the fuel-air mixture is at or above the operating temperature, a starter is controlled to facilitate smooth starting of the diesel engine and to bring the engine speed of the diesel engine into be a steady state value. That is, ignition of the fuel-air mixture may not be successful in an earlier stage of the diesel engine starting in which the diesel engine is as cold as the fuel-air mixture, since compression heat is not sufficient.
As an apparatus for controlling energization to the glow plug, a glow plug energization control apparatus is known. Ideally, the temperature of the glow plug should be rapidly raised up to the ignition temperature of the fuel-air mixture prior to the initial actuation of the diesel engine. The sufficiently heated glow plug serves to heat the fuel-air mixture around the glow plugs up to the ignition temperature.
The step as stated above is generally called a pre-glow or pre-glow step. In the pre-glow step, a large electric power is supplied to the glow plug. When the starter switch is turned on to facilitate starting the diesel engine at the end of the pre-glow step, the diesel engine can be started for smooth and continuous running.
After the temperature of the glow plug has reached to the operating temperature, smaller electric power than that in the pre-glow step is supplied from a battery to the glow plug so as to prevent the temperature of the glow plug from dropping. This step just is called an after-glow or after-glow step. In this after-glow step, it is possible to prevent the occurrence of dropping of the temperature in the combustion chamber of the diesel engine and the occurrence of diesel knock, and to suppress the occurrence of noise and white smoke, the exhaustion of HC composition, and the like because the fuel-air mixture is completely burned.
In the after-glow step, electric power supply to the glow plug is performed under a pulse width modulation (PWM) control. A voltage applied to the glow plug can be changed step-wise between a high level and a low level in a cyclic operation with a short periodic time. A duty ratio is defined as herein the ratio of a time interval when a voltage applied to the glow plug is at high level versus a further time interval when a voltage is at low level. Therefore, a voltage applied to the glow plug under a 100 percent PWM operation is a time-invariant constant. One of the merits of the PWM control is that electric power supplied to the glow plug can be easily adjusted in accordance with the duty ratio.
When the key switch is turned on, a conventional diesel engine control system having a glow plug control apparatus has been adapted to control electric power supply such that electric power is supplied to the glow plug and the glow plug control apparatus. The glow plug control apparatus controls electric power supply from a battery mounted on a vehicle to the glow plug prior to starting the engine in order to heat the glow plug. This leads to the raising of the temperature in a combustion chamber of the diesel engine up to the efficient operating temperature as rapidly as possible. At the same time, the glow plug control apparatus controls electric power supply to actuate the electromagnetic drive actuators of an injection pump to control for adjusting the amount and timing of fuel injection and to control starting of the engine so as to crank up the non-operating engine by supplying electric power to the starter in accordance with the results of monitoring the engine conditions.
Usually, a large inrush current is applied to the glow plug and the starter immediately after starting flowing electric current through them. Sometimes a large inrush current can be passed through the glow plug on the order of several ten times the steady state electric current.
Recently, low-rated-voltage type glow plugs are widely used in order to improve the start-up reliability and the rate of rise of the glow plug temperature even in the situation where an applied voltage is low due to the low capacity of a battery mounted on a modern highly-electronified vehicle. However, the very large inrush current is unavoidably applied to the low-rated-voltage type glow plugs because of the low initial resistance thereof.
In actuating the engine when generators which are driven by the rotary torque from the engine can not output any electric power, actuators for starting up the diesel engine such as glow plugs, starters, and injectors for fuel injection are supplied electric power from only the battery. The battery does not generally have redundant capacity.
Therefore, in very cold weather, an internal electric resistance of the battery is increased. This phenomena leads to the reduction of an output voltage of the battery, and to the failure of starting up the diesel engine since the glow plugs and the starter can not be supplied enough electric power from the battery to work efficiently.
Even when the output voltage of the battery is kept at a normal level, coinciding the starting timing of both preheating of the glow plug and starter ignition may result in expediting the consumption of the battery because of the large scale of the inrush current flowing through both the glow plug and starter. The starter can facilitate starting engine by outputting a sufficiently large torque. However in this case, the diesel engine may sometimes fail to start since sufficient electric power for heating the glow plug and for driving the starter is not obtained.
One of the methods for overcoming the above mentioned difficulties is to increase the battery size to improve the battery capacity. It is difficult to use this method because there is no room for the bigger battery to be located in the engine room for the modern complicated engine system.
Accordingly, it is required to adjust electric power supply to the glow plug, the starter, and the actuators for starting up the diesel engine for the sake of working all of these elements well.
A method for reducing the load on the battery is disclosed in Japanese Patent Laid-Open 2003-65195, U.S. Pat. No. 6,722,334, and German Patent Publication No. 10138997. This method is designed so that actuation of the starter is delayed beyond the beginning of the preheating such that the preheat peak load occurs before the starter peak load.
A diesel engine control system for reducing the load on the battery is disclosed in Japanese Patent Laid-Open 9-032606 and British Patent First Publication No. 2,303,470. In this diesel engine control system, electric power from the battery is not supplied to the fuel injection actuators until an energization-stop time after the glow plug has been switched on. The energization-stop time is calculated based on the cooling water temperature of the diesel engine. If the starter switch is turned on within the energization-stop time, the controller of this diesel engine control system starts supplying electric power to the fuel injection actuator from the battery.
A further method for reducing the load on the battery is disclosed in U.S. Pat. No. 6,637,932 and Korean Patent Publication No. 2002-0022359. In this method, electric power supply to the glow plug is controlled based on injected fuel, engine speed and cooling water temperature so as to prevent unnecessary electric power consumption of the battery even after the engine successfully starts.
An operator of the vehicle usually turns the switch on to attempt to start the engine. Thus, he or she does not consider the status of the battery which supplies electric power to the glow plug.
Therefore, when the glow, plug controller is designed, for example, to delay actuation of the starter as mentioned above, the operator's attempt for starting the engine dose not coincide with the timing of actuation of the starter. In this case, the operator of the vehicle often turns off the starter switch and immediately turns it on again because he has the mistaken recognition that the engine trouble was occurred. This leads to unnecessary electric power consumption of the battery.
In a case where the low-rated-voltage type glow plug is used and all the starting timing of preheating the glow plug, starter ignition and injectors for fuel injection coincide, or in further case where the excess inrush current flowing through the glow plug is not suppressed sufficiently after the preheating peak load occurs, it is impossible to start up the diesel engine because, in addition to a large inrush current supplied to the starter, another large current is required to start the actuators for starting up the diesel engine. In this situation however another large current can not be obtained from the battery.
Besides, when electric power is supplied to the glow plug during the pre-glow step for only starting the engine, the surrounding temperature of the glow plug, such as the temperature of an engine block and a main body metal fitting, remains at a low level just after the engine is started. Then the temperature of the glow plug is dropped since the temperature of the glow plug is absorbed by these elements. In this state, even if the key switch is put in a start position to start cranking, the engine is hard pressed to start smoothly since the temperature of the fuel-air mixture dose not reach at the operating temperature, or diesel knock and incomplete combustion may occur.